Paneled air filters are commonly used for filtering air in forced air systems such as Heating, Ventilation and Air Conditioning systems, commonly known as HVAC, as well as air intakes for gas turbines, or industrial process applications for filtering air. Panel air filters generally comprise a rectangular filter media pack supported by a support structure in a rectangular configuration such as being surrounded and supported by a die cut paper board panel frame or by strips, bands, scrims, screens or the like, and/or by plastic header frames.
One common type of filter media used in panel filters is pleated filter media that includes a plurality of peaks and valleys. Various prior art implementations are known to support pleated filter media so that the panel filters may withstand air pressure during operation. Such prior art includes U.S. Pat. No. 6,709,480 to Sundet et al.; U.S. Pat. No. 5,782,944 to Justice; and U.S. Patent Publication Number 2007/0294988, and US 2014/0165839 to Crabtree, both assigned to the present assignee, the entire disclosures of all of which are hereby incorporated by reference thereto.
Generally, in panel filter implementations, there are competing interests involved. On the one hand, a panel filter must provide sufficient dust holding capacity without plugging prematurely to provide adequate filter life span. Additionally, the filter has to provide a suitable particle capture efficiency by removing sufficiently small particles such as dust and allergens from the air that are known to be entrained in such forced air ventilation systems.
In some applications, a Minimum Efficiency Reporting Value (MERV) value of at least 13 or greater is desired.
In other applications such as pre-filters with downstream finishing filters, a lower MERV value is acceptable such as 8, as in the case of pre-filters for air intakes for gas turbines. The present application has applicability to these applications too.
For both highly efficient filters and less efficient filters, having a high dust load capacity is desirable.
In such applications, on the other hand, it is desirable not to restrict the flow of air and thereby provide for an open filter structure that allows for easy air flow through the pleated panel filter. The primary reason is that plugging is determined by the pressure drop that is experienced across the filter. Additionally, restricting airflow makes it harder for an HVAC system to deliver hot, cold and/or ventilated air resulting in energy loss. One test for determining the service life of a filter is evaluating dust holding capacity of the filter when the final resistance or pressure drop across the filter reaches 1.5 inch (3.8 cm) in water gauge pressure at a face velocity of 492 feet (150 meter) per minute, which is a standard ASHRAE 52.2-2012 test. Thus, while a restrictive media is desired so as to enable adequate particle capture efficiency, a more open media is desired for air flow characteristics and to prevent premature clogging.
As a result, prior art panel filters have often been a compromise between these two competing interests.